Preflight & class schema

Preflight checks whether sources are usable before spatial or temporal processing. It also writes a reusable class schema that can be edited and fed back into later engines.

Inputs and parameters

Parameter	Required?	Meaning / effect
Reference/grid raster	Recommended	Used to check CRS, extent overlap, pixel size, origin alignment and extremely small/invalid rasters.
Main/reference vector label layer	No	Main vector source for class-field checks and class extraction.
Main/reference raster label layer	No	Main raster source for raster class-value extraction and grid checks.
Additional vector/raster sources	No	Extra sources checked against the same reference conventions where possible.
Reference class field	Required for vectors	Attribute containing the class/code to burn later. HELIX refuses broad fallback fields such as `id` or the first attribute.
Class schema file or opened table	No	Existing CSV/JSON/QGIS table schema to validate and merge. Useful for remapping strings/raster IDs.
Treat raster value 0 as class	No	Use this for binary/zero-based class rasters where 0 is not background.

Core checks

y_out(x) = m(y_in(x))

Remapping: the class schema defines the mapping m from source values to target class IDs. This applies to vector attributes and raster pixel values.

overlap = area(E_ref ∩ E_src) / area(E_ref)

Extent check: E_ref is the reference extent and E_src is the source extent. Very small or zero overlap indicates a wrong CRS, wrong file or wrong study area.

δ_x = ((x_0,src − x_0,ref) / Δx_ref) mod 1

δ_y = ((y_0,src − y_0,ref) / Δy_ref) mod 1

Grid alignment: near-zero offsets mean that source and reference grid origins lie on compatible pixel grids. Misalignment is not always fatal, but it can create categorical resampling artefacts.

Class schema columns

Column	Meaning
`source_value`, `source_class_id`, `pixel_value`, `old_id`, `from`	Input value from vector attribute or raster pixel.
`target_class_id`, `new_class_id`, `class_id`, `to`	Output class value. Use this for remapping or merging.
`class_name`	Human-readable label name.
`include`	Optional include flag. False/0/no can exclude a class when later engines use “Included in schema”.
`quality_q`	Optional per-class quality prior used by Soft targets & weights.
`priority`	Optional source/class priority for reportable workflows.

Outputs

Output	Use
Preflight JSON	Machine-readable report for scripts and issue tracing.
Preflight HTML report	Human-readable audit of sources, CRS, grid, classes and warnings.
Class schema CSV/JSON	Edit this table to remap classes, names, quality and include flags.